1. Field of the Invention
This invention relates generally to loudspeakers, and in particular to a system for controlling the frequency response of a horn loudspeaker.
2. Related Art
In general multi-way loudspeaker systems are well known. Typical examples of multi-way loudspeaker systems include two-way loudspeakers and three-way loudspeakers. Generally, multi-way loudspeaker systems include multiple transducers (generally referred to as “loudspeakers,” “speakers,” “sound drivers,” or “drivers”) that operate at different frequency ranges. As an example, typical two-way loudspeakers include a low-frequency transducer and a high-frequency transducer, while typical three-way loudspeakers include a low-frequency transducer, a mid-frequency transducer (generally known as “midrange transducer” and “midrange driver”), and a high-frequency transducer.
In FIG. 1, a perspective view of an example of an implementation of a known three-way loudspeaker 100 is shown. In this example, the three-way loudspeaker 100 may include a housing 102, one or more low-frequency transducers (not shown) behind some sound baffles 104, one or more mid-frequency transducers (not shown) located behind one of more sound integrators (such as for example a “radiation boundary integrator” (“RBI”)) 106 to control sound, and one of more high-frequency transducers (not shown) connected to one or more sound waveguides (also known as high-frequency horns) 108. This example is more fully described by U.S. Pat. No. 7,324,654, titled “Arbitrary Coverage Angle Sound Integrator,” filed on Jul. 1, 2003 and U.S. Pat. No. 7,134,523, titled “System For Integrating Mid-Range and High-Frequency Acoustic Sources In Multi-way Loudspeakers,” filed on Nov. 22, 2002, both of which are herein incorporated by reference in their entirety. This example is also implemented in a product known as JBL® VerTec VT4889 produced by Harman International Industries, Inc. of Stamford, Conn.
Turning to FIG. 2, a exploded side-view of an example of an implementation of a high-frequency transducer 200 and two mid-frequency (also known as “mid-range”) transducers 202 and 204 within the three-way loudspeaker 100 of FIG. 1 is shown. The high-frequency transducer 200 is connected to a high-frequency horn 206, which is a sound waveguide, via the horn driver side 208. The high-frequency transducer 200 is also known as a high-frequency driver. The high-frequency horn 206 and mid-frequency transducers 202 and 204 are connected to sound integrators 210 and 212, respectively. The high-frequency horn 206 is connected to the sound integrators 210 and 212 at an open end 214 of the high-frequency horn 206 that is opposite the horn driver side 208. In this example, the sound integrators 210 and 212 may act as flares of the high-frequency horn 206 and are described in U.S. Pat. Nos. 7,134,523 and 7,324,654. The sound integrators 210 and 212 includes mating members (not shown) for engagement with the mid-frequency transducers 202 and 204, respectively. The high-frequency horn 206 is a horn loudspeaker element that uses a horn to increase the overall efficiency of the high-frequency transducer 200 (also known as “driving element”).
The high-frequency horn 206 is a passive component and does not amply the sound from the high-frequency transducer 200 but rather improves the coupling efficiency between the high-frequency horn 206 on the horn driver side 208 and the air on the open end 214. The high-frequency horn 206 may be thought of as an “acoustic transformer” that provides impedance matching between the relatively dense diaphragm material(s) (not shown) of the high-frequency transducer 200 at the horn driver side 208 to the air of low density at the open end 214. The result is greater acoustic output from the high-frequency transducer 200. The high-frequency horn 206 is generally a hollow tube, or pipe, defining an empty chamber (also known as a “cavity”) (not shown) volume between the horn driver side 208 and open end 214. The high-frequency horn 206 includes a surface wall 216 that defines the empty chamber of the high-frequency horn 206 and tappers from a narrow part of the high-frequency horn 206 at the horn driver side 208 to large part of the high-frequency horn 206 at the open end 214. The tapering part of the surface wall 216 is typically known as “flare” of the horn. Generally, the narrow part of the narrow part of the high-frequency horn 206 at the horn driver side 208 is known as the “throat” of the high-frequency horn 206 and the large part of the high-frequency horn 206 at the open end 214 is known as the “mouth” of the high-frequency horn 206.
In FIG. 3, a top assembly-view of an example of an implementation of a high-frequency transducer 200, high-frequency horn 206, and sound integrators 210 and 212 is shown. The sound integrators 210 and 212 include mounting mechanisms 300 and 302, respectively, positioned on the rear of the sound integrators 210 and 212 to permit the mounting of mid-frequency transducers (not shown).
Turning to FIG. 4, a cross-section view of an example of an implementation of two high-frequency horns 400, 402, and a sound integrator 404 is shown. The throats of the two high-frequency horns 400, 402 includes mating members 406 and 408, respectively, for engagement with a high-frequency transducer (such as for example, high-frequency transducer 200) and, at the opposing end (i.e., the mouth of the high-frequency horns 400 and 402), opens to sound integrator 210 which may act as a continuation of the horn flare of the high-frequency horns 400 and 402. Optionally, vanes (not shown) may be included within the empty chambers 410 and 412, respectively, of the high-frequency horns 400 and 402 (i.e., between the mouth and throats of the high-frequency horns).
In an example of operation, the high-frequency transducer 200 injects the high-frequency horn 206 with high-frequency sound waves 218 that travels through the high-frequency horn 206 and is output from the open end 214 of the high-frequency horn 206. The high-frequency horn 206 converts large pressure variations with a small displacement area at the horn driver side 208 into a low pressure variation with a large displacement area at the open end 214, and vice versa. The high-frequency horn 206 does this through the gradual, often exponential increase of the cross sectional area of the high-frequency horn 206 from the horn driver side 208 to the open end 214. The small cross-sectional area of the throat at the horn driver side 208 restricts the passage of air thus presenting a high impedance to the high-frequency transducer 200. This allows the high-frequency transducer 200 to develop a high pressure for a given displacement. Therefore the high-frequency sound waves 218 at the throat are of high pressure and low displacement. The tapered shape of the high-frequency horn 206 allows the high-frequency sound waves 218 to gradually decompress and increase in displacement until they reach the mouth at the open end 214 where they are of a low pressure but large displacement.
Simultaneously, the mid-frequency sources 202 and 204 inject sound integrators 210 and 212, respectively, with mid-frequency sound waves 220 and 222, respectively, that pass through the sound integrators 210 and 212. The combination of the high-frequency sound waves 218 and mid-frequency sound waves 220 and 222 produce combined output sound wave(s) 224 in the far-field of three-way loudspeaker 100. The combined output sound wave 224 may also include the low-frequency sound waves (not shown) produced by the low-frequency transducers (not shown) described in FIG. 1.
Unfortunately, in this example, a portion of the mid-frequency sound waves 220 and 222 is transmitted into the open end 214 of the high-frequency horn 206. As such, leaked sound waves 224 and 226 enter the high-frequency horn 206. The high-frequency horn 206 acts as a closed pipe to the leaked sound waves 224 and 226 and the midrange acoustical energy from the leaked sound waves 224 and 226 form standing waves in the high-frequency horn 206 at various frequencies. Unfortunately, the formation of these acoustical standing waves result in “dips” in the far-field midrange frequency response of the combined output sound waves 224 due to acoustical cancelation at the frequencies where the “dips” occur. A need therefore exists for a multi-way loudspeaker design that corrects the resulting dips in the far-field midrange frequency response caused by the standing waves in the high-frequency horn 206.